Double column multiple condenser-reboiler high pressure nitrogen process

Abstract

A cryogenic process to efficiently produce large quantities of nitrogen gas at elevated pressure by use of a double column and multiple condenser-reboilers.

We claim: 
     
       1. A process for the production of relatively large quantities of nitrogen gas at greater than atmospheric pressure by the separation of air by rectification comprising: (A) introducing cleaned, cooled feed air at greater than atmospheric pressure into a high pressure column operating at a pressure of from about 80 to 300 psia;   (B) separating said feed air by rectification in said high pressure column into a first nitrogen-rich vapor fraction and a first oxygen-enriched liquid fraction;   (C) recovering from about 20 to 60 percent of said first nitrogen-rich vapor fraction as high pressure nitrogen gas at a pressure in the range of from 80 to 300 psia;   (D) introducing said first oxygen-enriched liquid fraction into a medium pressure column which is in heat exchange relation with said high pressure column and is operating at a pressure lower than that of said high pressure column of from about 40 to 150 psia and in which feed introduced into said medium pressure column is separated by rectification into a second nitrogen-rich vapor fraction and a second oxygen-enriched liquid fraction;   (E) recovering from about 0 to 60 percent of said second nitrogen-rich vapor fraction as medium pressure nitrogen gas;   (F) condensing a portion of said first nitrogen-rich vapor fraction by indirect heat exchange with a portion of said second oxygen-enriched liquid fraction thereby producing a first nitrogen rich liquid portion and a first oxygen-enriched vapor portion;   (G) employing at least some of said first nitrogen-rich liquid portion as liquid reflux for said high pressure column and said first oxygen-enriched vapor portion as vapor reflux for said medium pressure column;   (H) condensing at least a portion of said second nitrogen-rich vapor fraction by indirect heat exchange with a portion of said second oxygen-enriched liquid fraction thereby producing a second nitrogen-rich liquid portion and second oxygen-enriched vapor portion;   (I) employing said second nitrogen-rich liquid portion as liquid reflux for said medium pressure column;   (J) employing said first nitrogen-rich liquid portion as additional liquid reflux for said medium pressure column in an amount equivalent to that of from about 0 to 40 percent of said first nitrogen-rich vapor fraction such that the sum of said amount and of the high pressure nitrogen gas recovered in step (C) is from about 20 to 60 percent of said first nitrogen-rich vapor fraction; and   (K) removing from the process said second oxygen-enriched vapor portion.   
     
     
       2. The process of claim 1 wherein all of said first nitrogen-rich liquid portion of step (G) is employed as liquid reflux for said high pressure column. 
     
     
       3. The process of claim 1 wherein in step (C) from about 30 to 50 percent of said first nitrogen-rich vapor fracion is recovered as high pressure nitrogen gas. 
     
     
       4. The process of claim 1 wherein in step (C) from about 35 to 45 percent or said first nitrogen-rich vapor fraction is recovered as high pressure nitrogen gas. 
     
     
       5. The process or claim 1 wherein said high pressure column is operating at a pressure of from about 90 to 240 psia. 
     
     
       6. The process or claim 1 wherein said high pressure column is operating at a pressure of from about 100 to 200 psia. 
     
     
       7. Tne process of claim 1 wherein said medium pressure column is operating at a pressure of from about 45 to 120 psia. 
     
     
       8. The process of claim 1 wherein said medium pressure column is operating at a pressure of from about 50 to 90 psia. 
     
     
       9. The process of claim 1 wherein in step (D) said first oxygen-enriched liquid fraction is introduced into said medium pressure column at the bottom of said column. 
     
     
       10. The process or claim 1 wherein in step (D) said first oxygen-enriched liquid fraction is introduced into said medium pressure column above the bottom of said column. 
     
     
       11. The prooess ot claim 1 wherein a part of the first nitrogen-rich vapor fraction is removed from the high pressure column, expanded, and introduced into the medium pressure column. 
     
     
       12. The process or claim 1 wherein a nitrogen-rich vapor stream is removed from said medium pressure column at a point intermediate the respective points where said first oxygen-enriched liquid fraction and said second nitrogen-rich liquid portion are introduced into said medium pressure column, and is warmed, expanded and removed from the process. 
     
     
       13. The process of claim 1 wherein in step (E) from about 20 to 50 percent of said second nitrogen-rich vapor fraction is recovered as medium pressure nitrogen gas. 
     
     
       14. The process of claim 1 wherein in step (E) from about 35 to 45 percent of said second nitrogen-rich vapor fraction is recovered as medium pressure nitrogen gas. 
     
     
       15. The process or claim 1 wherein in step (J) said sum is from about 30 to 50 percent of said first nitrogen-rich vapor fraction. 
     
     
       16. The process of claim 1 wherein said second oxygen-enriched vapor portion is recovered as product oxygen. 
     
     
       17. The process of claim 1 wherein at least a portion of said second oxygen-enrich vapor portion is warmed and expanded prior to removal from the process. 
     
     
       18. The process or claim 1 wherein an amount of air in excess of what is required as feed air is expanded, warmed by indirect heat exchange with feed air, and removed from the process.